It does not sound like he is working on anything, especially with the "get over it" attitude, except his own desires.

I would get over him; file for divorce and make sure he doesn't have extra time or money; he'll be so busy working to support his children and you with your pregnancy that he won't be able to afford a cell phone, much less a texting package so he can cheat.

I'm sorry you have such a difficult problem now when you have other things going on as well. Convert that sadness to anger that he would treat you and your children this way and act on that anger to make sure the children are cared for by him and you have enough support (from all good sources you can find) to get you through your pregnancy and into training or work to help.